This invention relates to shower heads for delivering gases to reactor chambers.
In many processes, such as plasma etching, chemical vapour deposition and plasma enhanced vapour deposition, it is desirable to introduce into a reactor chamber two or more gases or vapours relatively evenly throughout the chamber. This is generally achieved by a device known as a shower head and typically these comprise a casing defining a volume and having an outlet plate defining a plurality of openings. However in some processes it is necessary to deliver the gases or vapours in such a way that the gases are delivered, but not mixed until they enter the chamber. This is frequently achieved by a baffle plate that extends across the volume defined by the showerhead casing to define first and second gas plena or respective sides thereof. The first plenum is on the outlet side of the baffle plate and is essentially defined between a series of tubes, which project downwardly from the baffle plate to communicate the second plenum (on the other side of the baffle plate) with the openings in the outlet plate. An apertured rubber gasket is provided between the outlet plate and the ends of the tubes to seal the passages defined by the tubes from the first plenum. Where a tube engages the rubber gasket, gas can pass through the openings in the gasket and the aligned openings in the outlet plate. The other openings in the gasket serve to communicate the first plenum with their associated openings in the outlet plate.
This design creates a number of problems. Firstly the gasket must be accurately matched up to the holes in the outlet plate and a certain pressure is need to maintain a seal between the outlet plate and the gasket. It is preferred that the outlet plate is made with aluminium, because it is suitable for many processing reasons, but aluminium is relatively flexible and it has become progressively more difficult to maintain a good seal as shower head dimensions have increased along with the increase in the dimensions of the wafers to be processed. Attempts to overcome these problems using fastenings have disrupted the continuous surface of the outlet plate and are potential sources of contamination, particle generation and lack of uniformity of processing. Further on occasions a plasma can ignite within the cavities of the shower head causing damage to the gasket and plasma activity can react with any iron-based fastenings within the shower head causing contamination.